is the squat jumper. start in the down squatting position,ass resting on the heel of one of your feet, the other foot is forward of your rear foot flat on the ground. your hands are locked behind your head. count one you rocket upwards, coming 8 inches off the ground, achieving a verticle position in the air, and switch your feet, the rear foot becoming the front foot and the front the rear, when you land, go back down to the squatting position with your butt on your rear foot. repeat for 3 more counts. that is one repitition. 10 reps will kick your ass, 30 will just about kill you. be sure to keep your back straight, and keep proper form.